A borane-based optical fiber fluorescent sensor for detecting low concentrations of formaldehyde

Abstract

The application discloses a decaborane-based optical fiber fluorescence sensor for detecting low-concentration formaldehyde, introduces 5-aminoisoquinoline groups into a decaborane matrix, and first synthesizes a decaborane-based formaldehyde fluorescence probe. The fluorescence response performance of the probe to formaldehyde is tested through fluorescence spectrum. The probe has an enhanced response to formaldehyde in a solution in a large concentration range of 0-600 muM, and the detection limit is 4.18*10 ‑ 6 M. The formaldehyde fluorescence probe has the advantages of good linearity, strong anti-interference and high sensitivity. The application constructs an optical fiber formaldehyde fluorescence sensor based on a M1 / PMMA film, and the detection limit of the optical fiber fluorescence sensor to formaldehyde is improved to 6.9*10 ‑8 M. The optical fiber fluorescence sensor is successfully used for detecting formaldehyde in food and water solution, and the result is reliable. The optical fiber fluorescence sensor has the advantages of good selectivity, low detection limit, on-line and remote monitoring, and the like, and has a good application prospect in the field of formaldehyde detection in chemical industry, biology, environment and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of formaldehyde detection, and particularly relates to a decaborane-based optical fiber fluorescence sensor for detecting low-concentration formaldehyde. BACKGROUND

[0002] Formaldehyde (FA) is a small molecule with carbonyl structure, which has attracted extensive attention in recent years because it is confirmed to be an extremely important ring in biological metabolism. Formaldehyde is involved in biological carbon metabolism, energy generation and signal pathway, and affects its growth process. On the other hand, formaldehyde taken from the environment can cause protein and DNA denaturation. Studies have shown that the human body can produce low-concentration endogenous formaldehyde, which can participate in the regulation of human gene expression and cell signal transduction, and affect human memory and cognitive ability. In addition, diseases such as cancer, asthma and multiple sclerosis are related to endogenous formaldehyde, and the overexpression or non-expression of endogenous formaldehyde affects human health. However, the generation and consumption of endogenous formaldehyde are usually at the sub-millimolar level. Therefore, it is very important to develop a simple, rapid and low-concentration formaldehyde detection method.

[0003] Formaldehyde is closely related to human health, and it is very important to accurately monitor the concentration of formaldehyde in the environment. Traditional formaldehyde detection methods mainly include gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), colorimetry, UV-vis spectrophotometry, and electrochemical analysis detection method. However, these methods require the use of expensive instruments and have high requirements for the operating personnel. In recent years, fluorescence detection technology gradually stands out in the detection field due to its high sensitivity, easy sample preparation, good selectivity, and real-time monitoring. The structure of a fluorescent probe is composed of a fluorescent group, a recognition group, and a connecting unit, and the fluorescent group determines the sensitivity of the probe. Commonly used fluorescent groups include rhodamine, fluorescein, coumarin, quinoline, naphthalene amidite, BODIPY, and cyanine. The pyridine derivative of decaborane has good coloring effect and high fluorescence quantum yield, and so far there has been no report on the fluorescent probe based on decaborane. In recent years, fluorescent probes for detecting formaldehyde have attracted widespread attention. Zheng and Priyadarsi De groups summarized the latest progress of formaldehyde fluorescent probes. The mechanism of the fluorescent probe for detecting formaldehyde is mainly based on simple amino and hydrazine groups as reaction groups, which change the fluorescence intensity of the molecule to realize the detection of formaldehyde by generating imine and methylene hydrazine after reacting with formaldehyde. In addition, the aza-Cope rearrangement, i.e. [3,3]-sigmatropic rearrangement, is also a way to detect formaldehyde. Chan group developed the first formaldehyde probe based on aza-Cope rearrangement in 2015, and the probe was successfully used for imaging of formaldehyde in living cells. However, the detection limit of the above formaldehyde probe is 10 -6 M-10 -7 M order of magnitude, and it is difficult to detect lower concentration of formaldehyde. Therefore, another way is needed to realize the detection of extremely low concentration of formaldehyde. Optical fiber sensing technology has the advantage of low detection limit, and the detection limit of optical fiber ion sensing can be as low as 10 -11 M. However, there is no report on optical fiber sensor for detecting formaldehyde. SUMMARY

[0004] Therefore, in order to solve the problems in the prior art, the present application provides a decaborane-based optical fiber fluorescent sensor for detecting low concentration of formaldehyde. A fluorescent probe based on decaborane derivative is designed and synthesized, and on the basis of detailed study on the performance of the fluorescent probe, an optical fiber formaldehyde fluorescent sensor based on Mach-Zehnder structure and M1 / PMMA film is constructed. The detection limit of the sensor for formaldehyde can be reduced from 4.18 x 10-6 M is reduced to 6.9*10 -8 M, the sensor is successfully used for detecting formaldehyde in food samples, and the accuracy of the results is verified by comparison with the acetylacetone method.

[0005] The present application solves the above problems by the following technical means:

[0006] A decaborane-based optical fiber fluorescence sensor for detecting low-concentration formaldehyde, comprising a broadband light source, an optical fiber sensor, and a spectrum analyzer;

[0007] The broadband light source is used to generate incident light, and the spectrum analyzer is used for collection and processing of optical signals; the optical fiber sensor comprises three sections of single-mode optical fiber and two sections of coreless optical fiber, which are connected in the order of a first section of single-mode optical fiber, a second section of coreless optical fiber, a third section of single-mode optical fiber, a fourth section of coreless optical fiber, and a fifth section of single-mode optical fiber; the third section of single-mode optical fiber for sensing is coated with a sensing film and serves as a sensing optical fiber; a decaborane-based formaldehyde fluorescence probe solution is added to a film-forming solution of the sensing film during preparation of the sensing film;

[0008] The incident light emitted by the broadband light source passes through the sensing optical fiber coated with the sensing film, and the output light is collected by the spectrum analyzer; the second section of coreless optical fiber serves as a beam splitter to disperse the incident light emitted by the broadband light source; when the incident light passes through the sensing optical fiber, more than 1 / 2 of the light still propagates in the core of the sensing optical fiber, and the other part of the light propagates in the cladding of the sensing optical fiber; the light propagating in the cladding is regulated by the sensing film, and when the two light beams reach the fourth section of coreless optical fiber, interference occurs; finally, the interference light is collected by the spectrum analyzer and an interference spectrum is output.

[0009] Preferably, the decaborane-based optical fiber fluorescence sensor for detecting low-concentration formaldehyde further comprises a programmable temperature controller for temperature control, and the optical fiber sensor is placed in the programmable temperature controller during use.

[0010] Preferably, in the decaborane-based optical fiber fluorescence sensor for detecting low-concentration formaldehyde:

[0011]

[0012] wherein I is the light intensity of the light emitted by the broadband light source, I core is the light intensity passing through the core, cladding is the light intensity passing through the cladding, is the difference in light intensity of the two light beams, L is the length of the third section of single-mode optical fiber of the optical fiber sensor, is the effective refractive index of the core, is the effective refractive index of the sensing film;

[0013] When At this time, the two beams of light passing through the core and the cladding undergo Mach-Zehnder interference;

[0014]

[0015] wherein m is the interference order, λ m is the wavelength of the interference peak.

[0016] As preferred, the decaborane-based formaldehyde fluorescent probe is synthesized by the following steps:

[0017] Dissolve decaborane in dry benzene and stir at room temperature until completely dissolved, then add diethyl sulfide to obtain a light yellow-green solution, and then heat the mixed solution under nitrogen protection for a certain period of time until the reaction is complete; after the reaction is completed, the solution is yellow, and after cooling to room temperature, add diethyl ether and pentane, then cool with ice, at this time a large amount of white crystals are precipitated, after vacuum filtration, obtain [(C2H5)2S]2B 10 H 12 ;

[0018] Dissolve [(C2H5)2S]2B 10 H 12 and 5-NH2C9H6N in dry benzene, respectively, after both are completely dissolved, add [(C2H5)2S]2B 10 H 12 to the 5-NH2C9H6N solution, and the mixture is reacted at room temperature under nitrogen protection for a certain period of time, after the reaction is completed, filter to obtain the solvent, and evaporate the solvent to obtain the crude product; pass the crude product through the column for a certain number of times to obtain the final product decaborane-based formaldehyde fluorescent probe;

[0019] The reaction formula is as follows:

[0020] B 10 H 14 + (C2H5)2S → [(C2H5)2S]2B 10 H 12

[0021] [(C2H5)2S]2B 10 H 12 + 5-NH2C9H6N → (5NH2C9H6N)2B 10 H 12 + (C2H5)2S

[0022] As preferred, the decaborane-based optical fiber fluorescent sensor determines the detection limit of formaldehyde by fluorescence titration method: configure multiple groups of decaborane-based formaldehyde fluorescent probe solutions and measure the fluorescence intensity at 549 nm, calculate the standard deviation of the blank sample; measure the fluorescence intensity at 549 nm of multiple decaborane-based formaldehyde fluorescent probe solutions after reaction with formaldehyde, and the detection limit of formaldehyde can be calculated by the following formula:

[0023]

[0024] Where σ is the standard deviation of the blank sample, and κ is the slope of the curve of fluorescence intensity-FA concentration at 549 nm;

[0025] The detection limit of the decaborylene fiber optic fluorescence sensor for detecting low concentrations of formaldehyde is calculated using the following formula:

[0026]

[0027] Where λ is the wavelength, C is the formaldehyde concentration, and S... C denoted as the sensitivity of the fiber optic fluorescence sensor, and ∈ represents the resolution of the spectrometer.

[0028] Preferably, the fabrication of the sensing film of the fiber optic sensor includes:

[0029] Preparation of film-forming solution: PMMA was dissolved in dichloromethane solution, decaborylformaldehyde fluorescent probe solution was added, and the solution was ultrasonically treated to obtain a homogeneous solution;

[0030] Fabrication of the sensing film: First, a groove capable of accommodating the sensing optical fiber is constructed on a polytetrafluoroethylene (PTFE) plate using hot melt adhesive; the clean optical fiber is fixed on the PTFE plate, and the cladding of the sensing optical fiber in the middle is etched with HF for a certain period of time, followed by rinsing with ultrapure water a certain number of times; the film-forming solution is dropped into the groove, and the optical fiber is slowly and uniformly rotated at a constant speed for a certain period of time; finally, the obtained sensing optical fiber is placed in the dark for a period of time.

[0031] Preferably, the third single-mode fiber used for sensing in the fiber optic sensor has a length of 25mm, and the coreless fiber has a length of 10mm.

[0032] Preferably, the optimal pH value for the decaborylformaldehyde fluorescent probe to detect formaldehyde is 7.4.

[0033] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0034] This invention introduces a 5-aminoisoquinoline group into a decaborane matrix, resulting in the first synthesis of a decaborane-based formaldehyde fluorescent probe (M1). The molecular structure of the probe and its response mechanism to formaldehyde were determined by theoretical calculations and 1H-NMR, 11B-NMR, HR-MS, and FT-IR. The fluorescence response performance of the probe to formaldehyde was tested by fluorescence spectroscopy. The probe exhibits enhanced response to formaldehyde in solution over a wide concentration range of 0-600 μM, with a detection limit of 4.18 × 10⁻⁶. -6M. The results show that the formaldehyde fluorescent probe has the advantages of good linearity, strong anti-interference ability, and high sensitivity. Based on this, the present invention constructs an optical fiber formaldehyde fluorescent sensor based on M1 / PMMA thin film, which improves the detection limit of formaldehyde to 6.9 × 10⁻⁶. -8 M, a fiber optic fluorescence sensor, has been successfully applied to the detection of formaldehyde in food and aqueous solutions, and its results are reliable compared to the acetylacetone method. This sensor offers advantages such as high selectivity, low detection limit, and the ability to perform online and remote monitoring, showing promising application prospects in formaldehyde detection fields such as chemical, biological, and environmental sciences. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the decaborylene fiber optic fluorescent sensor of the present invention for detecting low concentrations of formaldehyde;

[0037] Figure 2 This is a flowchart of the manufacturing steps of the sensing membrane of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of the decaborylformaldehyde fluorescent probe M1 of the present invention;

[0039] Figure 4 This is the mass spectrum of the M1 molecule;

[0040] Figure 5 This is a simulated mass spectrum of the M1 molecule;

[0041] Figure 6 This is the FI-IR spectrum of M1;

[0042] Figure 7 The diagram shows the HOMO and LUMO energy levels and electron density distributions of M1(a) / M2(b);

[0043] Figure 8 This is the normalized UV-Vis absorption and fluorescence emission spectrum of M1 in THF solution, c = 10 μM, λ ex =320nm;

[0044] Figure 9 These are diagrams showing the M1 recognition mechanism for formaldehyde and the fluorescence changes of the M1 molecule before and after formaldehyde recognition; where (a) is the recognition mechanism diagram of M1 and (b) is the luminescence mechanism diagram of M1.

[0045] Figure 10This is the FI-IR spectrum of M2;

[0046] Figure 11 This is a graph showing the change in fluorescence intensity over time for the reactions of M1 (10 μM) and FA (50 μM);

[0047] Figure 12 The images show the fluorescence spectra of M1 (10 μM) in THF / PBS (VPBS / VTHF = 5:5) at different pH values ​​and the relationship between M1 and pH. (a) shows the fluorescence spectra of M1 (10 μM) in THF / PBS (VPBS / VTHF = 5:5) at different pH values; (b) shows the relationship between M1 and pH.

[0048] Figure 13 This is a graph showing the relationship between formaldehyde concentration and fluorescence intensity (M1 10 μM);

[0049] Figure 14 The fluorescence intensity graphs of M1 (10 μM) after 10 min of reaction of different substances (50 μM);

[0050] Figure 15 This is a graph showing the determination of formaldehyde in food samples using the acetylacetone method.

[0051] Figure 16 The fiber optic sensor is used at different concentrations (2×10⁻⁶). -8 M-10×10 -8 M) Spectrum of formaldehyde solution and linear fitting graph of formaldehyde concentration and light intensity; where (a) shows the optical fiber sensor at different concentrations (2×10⁻⁶). -8 M-10×10 -8 (a) is the spectrum of formaldehyde solution, and (b) is the linear fitting graph of formaldehyde concentration and light intensity. Detailed Implementation

[0052] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] 1. Reagents and Instruments

[0054] 11 B NMR and 11H NMR spectroscopy was performed on a Bruker AVANCE NEO spectrometer. HRMS was performed on an LCMS-IT-TOF instrument at Shimadzu, Kyoto, JP. Spectrum Two was used to measure the FT-IR spectra of the samples. A Shimadzu UV 2700 spectrophotometer was used to obtain the UV spectra of the samples. Fluorescence spectroscopy of the samples was performed using a Hitachi F-4600 fluorophotometer (excitation and emission slit width 5 nm, voltage 700 V). The surface morphology of the sensing film was obtained using a Zeiss Gemini 500 scanning electron microscope. A spectrometer (OSA, ANDO AQ6370) (amplified spontaneous emission (ASE), wavelength range: 1520 nm-1620 nm) was used for light signal acquisition. A programmable temperature controller (Jiexin Test Equipment Co., Ltd., J-TOPH-22-B) was used for temperature control.

[0055] The supplier of decaborane was Zhengzhou Chemical Industry Co., Ltd., and other reagents were supplied by Aladdin-Reagent. All reagents were of analytical grade. Benzene reagents used in the experiment needed to be dried before use. Ultrapure water was used in the experiment.

[0056] 2. Synthesis of probe M1

[0057] The synthesis of probe M1 using decaborane as the starting material was achieved in two steps: (1) 2.945 g (0.024 mol) of decaborane was dissolved in 20 mL of dry benzene and stirred at room temperature until completely dissolved. Then, 8 mL of diethyl sulfide was added to obtain a light yellow-green solution. The mixed solution was heated to 78 °C under nitrogen protection and kept for 3 h to allow the reaction to complete. After the reaction was completed, the solution was yellow. After cooling to room temperature, an appropriate amount of diethyl ether and pentane were added, and then the solution was cooled with ice. At this time, a large amount of white crystals precipitated. After vacuum filtration, 4.269 g of [(C2H5)2S]2B was obtained. 10 H 12 (2) Weigh out 0.3g (0.001mol) of [(C2H5)2S]2B. 10 H 12 Dissolve 0.3604 g (0.0025 mol) of 5-NH2C9H6N in 20 mL of dry benzene. After both are completely dissolved, add [(C2H5)2S]2B. 10 H 12The mixture was added to a 5-NH₂C₉H₆N solution and reacted at room temperature for 4 h under nitrogen protection. After the reaction was complete, the solvent was filtered off, and the solvent was evaporated to obtain the crude product. The crude product was subjected to column chromatography (using CHCl₂:n-Hexane = 5:1) twice to give 0.0697 g of the final product M1, with a yield of 17%. ¹H NMR (600 MHz, DMSO) δ 9.60 (s, 1H), 8.55 (dd, J = 6.9, 1.1 Hz, 1H), 8.37 (d, J = 6.9 Hz, 1H), 7.81–7.39 (m, 2H), 7.32–6.80 (m, 2H), 6.70–6.24 (m, 3H), 1.22 (s, 2H), 0.87 (dt, J = 35.7, 7.2 Hz, 1H), -0.01 (s, 2H).

[0058] The reaction formula is as follows:

[0059] B 10 H 14 +(C2H5)2S→[(C2H5)2S]2B 10 H 12

[0060] [(C2H5)2S]2B 10 H 12 +5-NH₂C₉H₆N→(5NH₂C₉H₆N)₂B 10 H 12 +(C2H5)2S

[0061] 3. Calculation method

[0062] To investigate the relationship between the optical properties and electronic structure of molecules, the structure of the M1 molecule was simulated using Gauss09 software. All calculation results were derived from the theoretical simulations described above, and the molecular structure was optimized using DFT calculations at the B3LYP / 6-31G(d,p) level. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were obtained through calculation.

[0063] 4. Standard UV-Vis and fluorescence spectroscopy measurements

[0064] M1 was dissolved in THF solution for measuring ultraviolet and fluorescence spectra. The fluorescence spectra were measured under the following conditions: excitation and emission slit widths were 5 nm (λ). em =549nm, λ ex =320nm, 700V).

[0065] 5. Probe M1 is used for the detection of formaldehyde in solution.

[0066] 4.1 mg of M1 molecules were dissolved in 10 mL of THF to obtain a 0.1 M probe stock solution. Different concentrations of formaldehyde were added, and the solution was diluted with THF and phosphate buffer to the desired concentration (each test solution had a final volume of 2 mL and a probe concentration of 10 μM). Fluorescence spectra were recorded at an excitation wavelength of 320 nm. Simultaneously, a 10 μM probe solution and a 10 μM formaldehyde solution were prepared, and their fluorescence intensity was measured and recorded every 2 minutes. Mixtures of 10 μM M1 probe and different interfering substances were obtained using the same procedure, and their fluorescence spectra were recorded. Each solution was tested three times.

[0067] 6. Determination of formaldehyde detection limit

[0068] The detection limit of formaldehyde was determined by fluorescence titration: Five sets of M1 probe solutions were prepared and their fluorescence intensity at 549 nm was measured, and the standard deviation of the blank samples was calculated. The fluorescence intensity at 549 nm of the five M1 solutions after reacting with formaldehyde was measured, and the detection limit of formaldehyde was calculated using the following formula:

[0069]

[0070] Where σ is the standard deviation of the blank sample, and κ is the slope of the curve of fluorescence intensity-FA concentration at 549 nm.

[0071] The detection limit of the fiber optic fluorescence sensor is calculated using the following formula:

[0072]

[0073] Where λ is the wavelength, C is the formaldehyde concentration, and S... C denoted as the sensitivity of the fiber optic fluorescence sensor, and ∈ represents the resolution of the spectrometer.

[0074] 7. Determination of formaldehyde in food samples

[0075] The shiitake mushrooms, vegetables, and toffee used were all purchased from the local market. 5g of sample was weighed, pulverized, and added to 10mL of ultrapure water. The mixture was sonicated once and centrifuged three times to obtain the supernatant. Formaldehyde was added to the supernatant to prepare a series of sample solutions containing 0, 300, and 600 μM formaldehyde. Finally, 10 μM of probe molecules was added to each sample solution, and the fluorescence intensity was measured after reacting for 5 minutes.

[0076] 8. Structure of fiber optic fluorescence sensor

[0077] In this invention, the Mach-Zehnder structure is used to construct a fiber optic fluorescence sensor. The specific structure and beam transmission process of the fiber optic fluorescence sensor are as follows: Figure 1As shown, the system structure mainly consists of a broadband light source, an optical fiber sensor, a programmable temperature controller, and a spectrometer. The broadband light source generates the incident light, and the spectrometer collects and processes the optical signal. The optical fiber sensor uses single-mode fiber (SMF) and coreless fiber (NCF), connected in an SMF-NCF-SMF-NCF-SMF sequence: first segment single-mode fiber, second segment coreless fiber, third segment single-mode fiber, fourth segment coreless fiber, and fifth segment single-mode fiber. The intermediate SMF segment (coated surface) is 25mm long and serves as the sensing fiber, while the NCF segments are all 10mm long.

[0078] 9. Principle

[0079] The fiber optic sensor is placed in a programmable temperature controller, with the temperature set at 25°C. Light emitted from the amplified spontaneous emission broadband light source passes through the sensing fiber coated with a sensing film, and the output light is collected by a spectrometer. In this structure, the second coreless fiber acts as a beam splitter to disperse the light emitted from the ASE. When the light passes through the sensing fiber, most of the light still propagates in the core of the sensing fiber, while another portion propagates in the cladding (this portion is modulated by the sensing film). When the two beams reach the fourth coreless fiber, interference occurs, and the interfering light is finally collected by the spectrometer to output the interference spectrum.

[0080] The theoretical derivation is as follows:

[0081]

[0082] Where I is the light intensity of the emitted light from ASE, I core I is the light intensity passing through the fiber core. cladding The intensity of light passing through the cladding. Let L be the intensity difference between the two beams, and L be the length of the sensing fiber (the middle SMF fiber). The effective refractive index of the fiber core, The effective refractive index of the sensing film.

[0083] when At that time, the two beams passing through the fiber core and cladding undergo Mach-Zehnder interference.

[0084]

[0085] Where m is the interference order, λ m The wavelength of the interference peak.

[0086] 10. Fabrication of the sensing membrane for fiber optic sensors

[0087] Preparation of film-forming solution: Dissolve 300 mg PMMA in 8 mL of dichloromethane solution, add 4.1 mg M1, and sonicate to obtain a homogeneous solution.

[0088] The manufacturing steps of the sensing membrane are as follows: Figure 2 As shown, in order to uniformly coat the sensing film, a groove for accommodating the sensing fiber is first constructed on a polytetrafluoroethylene (PTFE) plate using hot melt adhesive; the clean fiber is fixed on the PTFE plate, and the cladding of the sensing fiber in the middle is etched with HF for about ten minutes, followed by rinsing three times with ultrapure water; 2 mL of the above film-forming solution is dropped into the groove, and the fiber is slowly and uniformly rotated at a constant speed for 5 minutes; finally, the obtained sensing fiber is placed in the dark for half an hour.

[0089] 11. Characterization of M1 structure

[0090] The structure of M1 is as follows Figure 3 As shown, high-resolution mass spectrometry (HRMS) and Fourier transform infrared spectroscopy (FT-IR) were used to verify the molecular structure of M1. Figure 4 It can be seen that the ion peak of M1 is 408.3311, which is basically consistent with the simulated value (408.3300) (e.g. Figure 5 As shown), the error in ppm (2.69) is within an acceptable range. Figure 6 It can be seen that the sample is at 3364.8 cm. -1 and 3475.4cm -1 Two characteristic absorption peaks appear, which are attributed to the stretching vibration of the NH bond in the amino group. 3211.1 cm⁻¹ -1 The absorption peak at 2508.3 cm⁻¹ originates from the stretching vibration of the BB bond. -1 The characteristic peaks are attributed to the stretching vibrations of the BH bonds. Notably, the sample shows a peak at 1192.9 cm⁻¹. -1 A new peak appeared, which is the bending vibration peak of the BN bond.

[0091] The energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a molecule determines its optical properties. The delocalized π electrons on the boron cluster of decaborane are easily transferred; introducing electron donors (D) and electron acceptors (A) into this structure is a common method for reducing the band gap. Therefore, the classic DA fluorophore—5-aminoisoquinoline—was introduced into the decaborane structure to obtain the M1 molecule. The frontier molecular orbital shape of M1 is as follows... Figure 7As shown, the calculated HOMO level of M1 is -4.01 eV, the LUMO level is -2.45 eV, and the energy difference is 1.55 eV. The HOMO is mainly located on the boron cluster, while the LUMO is mainly distributed on the two ligands, 5-aminoisoquinoline. This orbital distribution can be explained as an "inside-out" transfer mechanism. Similarly, the HOMO and LUMO levels of the product M2, formed after the reaction of M1 with formaldehyde, were calculated. The HOMO and LUMO levels of M2 are -4.81 eV and -2.59 eV, respectively, with an energy difference of 2.21 eV. After the reaction with formaldehyde, the fluorescence enhancement mechanism can be explained by frontier orbital theory. The photoinduced electron transfer (PET) process within the M2 molecule is inhibited, leading to enhanced fluorescence.

[0092] 12. Photophysical properties of M1

[0093] Figure 8 The normalized UV-Vis absorption and fluorescence emission spectra of M1 in THF solution are shown. Figure 8 It can be seen that M1 exhibits a strong emission peak at 549 nm and a weak emission peak at 640 nm. The strong peak at 549 nm has a large Stokes shift and a broad emission band, which is related to charge transfer within the M1 molecule, while the weak peak at 640 nm may be related to local excitation of the molecule. The UV-Vis absorption spectrum of M1 shows two broad absorption peaks near 300 nm and 371 nm, which are related to n-π* and π-π* transitions within the M1 molecule.

[0094] 13. Sensing mechanism of M1 probe for FA

[0095] B 10 H 14 It is a Nido-type borane structure, a square pyramidal aggregate structure missing a corner. Higher-order borane molecules have a cluster structure; the cluster fragments are three-dimensional multi-atom systems containing different BB bonds, with significantly delocalized valence electrons. The excited electrons of M1 can escape from |B 10 H 12 The delocalized π orbitals of the cluster are transferred to the antibonding π* orbitals on the 5-aminoisoquinoline aromatic heterocycle, thus the M1 probe molecule emits a weak yellow-green fluorescence under a 365nm UV lamp. Figure 9 (a) and (b) illustrate the mechanism by which M1 recognizes formaldehyde and the fluorescence changes of the M1 molecule before and after formaldehyde recognition. After the M1 probe reacts with formaldehyde, an imine is formed, the PET process of the molecule is inhibited, and M2 emits strong green fluorescence. To verify this reaction mechanism, Fourier transform infrared spectroscopy was performed on the product, and the results are as follows: Figure 10As shown, the two characteristic absorption peaks of the M2 molecule at 3364.8 and 3475.4 cm⁻¹ disappear, replaced by a peak at 2900 cm⁻¹. -1 A new C=N bond characteristic absorption peak appears at the point. Therefore, the detection mechanism of probe M1 for formaldehyde can be explained by the Schiff base reaction between the amino group on 5-aminoisoquinoline and formaldehyde to generate an imine, thereby inhibiting the PET process of the M1 molecule and leading to enhanced fluorescence.

[0096] 14. Optimization of detection conditions

[0097] To obtain the optimal detection performance of the probe, the fluorescence intensity of M1 molecules after reacting with formaldehyde at different pH and reaction times was tested. By monitoring the fluorescence change at 549 nm, the fluorescence intensity-time response curves of the M1 (10 μM) probe with five equivalents of formaldehyde were obtained, as shown below. Figure 11 As shown, when formaldehyde is added to the probe solution, the fluorescence intensity rises rapidly within 5 minutes, reaching its maximum at approximately 15 minutes. Therefore, fluorescence testing can be performed after 15 minutes of reaction. Compared with related reported work (Table 1), the response time of this invention has a significant advantage.

[0098] Table 1 Comparison of FA detection time with different probes

[0099] Probe Response time (min) Reference Publication date FA-P 180 [1] 2019 NFD 40 [2] 2023 QH-FA 10 [3] 2023 Probe 30 [4] 2021 Na-Hy 30 [5] 2022 CmNp-CHO 1 [6] 2022 Dm-FA 40 [7] 2023 Mito-FA-FP 20 [8] 2019 M1 5 The invention

[0100] A series of PBS buffers with different pH values ​​(50% THF, V) PBS / V THF =5:5) was used to study the effect of pH on the fluorescence intensity of M1, and the results are as follows Figure 12 As shown, the probe molecule exhibits strong and stable fluorescence intensity within a pH range of 5 to 10. Under strongly acidic conditions (pH 1 to 4), the amino group is protonated, resulting in a decrease in fluorescence intensity. Similar findings have been reported in formaldehyde detection using hydrazine groups as recognition groups. In strongly alkaline environments, the probe's fluorescence intensity drops sharply. Therefore, the optimal pH for M1 detection of formaldehyde is set at 7.4.

[0101] 15. Spectral response of probe M1 to FA

[0102] To determine the relationship between formaldehyde concentration and the fluorescence intensity of probe M1, the fluorescence intensity was measured in PBS buffer (pH = 7.4, 50% THF, V). PBS / V THF The fluorescence response experiment of M1 to FA was conducted in a ratio of 5:5. The optimal excitation wavelength of probe M1 was set to 320 nm. The results are as follows: Figure 13 As shown. Figure 13This indicates a weak fluorescence emission peak at 640 nm, with the largest emission peak appearing at 549 nm. As the formaldehyde concentration increased from 0 μM to 600 μM, the solution color gradually changed from yellow to light green, and the fluorescence intensity increased from 618.7 to 746.7, which is related to the intramolecular PET process. Linear fitting of the experimental results yielded R0. 2 The value is 0.9980, and the calculated limit of detection (LOD) for formaldehyde by M1 is 4.18 × 10⁻⁶. -6 Compared with most published works (Table 2), the formaldehyde detection limit of this invention has certain advantages. Therefore, the M1 probe has high sensitivity and low detection limit, and the color change of the solution after the addition of formaldehyde can be judged with the naked eye.

[0103] Table 2 Comparison of detection limits for different probes

[0104] Probe Detection limit (μΜ) Reference Publication date DM-FA 1.1 [7] 2023 FAP1 0.016 [9] 2023 QH-FA 0.0081 [3] 2023 NFD 0.95 [2] 2023 DBP 38

[10] 2023 Probe-NH2 1.87

[11] 2022 M1 0.069 The invention

[0105] The references mentioned in Tables 1 and 2 are as follows:

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[0117] 16. Selectivity of probe M1 for formaldehyde

[0118] To investigate the selectivity of M1 for formaldehyde, the fluorescence response of the M1 probe to various potential interfering substances was tested, including metal cations, silver ions, common organic compounds, and aldehydes. In this experiment, the probe concentration was 20 μM, and the concentration of the interfering substances was 100 μM. The results are shown below. Figure 14 .from Figure 14 As can be seen, the effect of interfering substances on formaldehyde is negligible; only formaldehyde enhances the fluorescence of the probe. Therefore, the probe has good selectivity for formaldehyde.

[0119] 17. Determination of formaldehyde in real food samples

[0120] The above experiments show that M1 exhibits a good fluorescence response to formaldehyde in the range of 0-600 μM, with a linear equation of FI = 0.21C + 619.64. This invention further evaluated the detection capability of M1 for real samples through experiments.

[0121] The fluorescence intensity of M1 after reacting with actual sample solutions of different concentrations was measured, and the results converted to formaldehyde concentration are shown in Table 3. Formaldehyde was detected in the shiitake mushroom sample, but its concentration was lower than the EU standard. Furthermore, the recovery rate was higher for the first two tests involving the shiitake mushroom sample. The fluorescence intensity of the blank samples from the other two food samples was comparable to that of the blank sample containing the pure probe, and no formaldehyde was detected. The recovery rate of formaldehyde in the three samples ranged from 96.48% to 127.82%, indicating relatively good recovery. Simultaneously, the formaldehyde concentration of the same sample was determined using the acetylacetone method for comparison, and the results are shown in Table 3. Figure 15 As shown, the error rate is 5.95%. Therefore, M1 can be used to quantitatively measure formaldehyde in food samples.

[0122] Table 3. Determination of formaldehyde in real food samples

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[0124] 18. Fiber optic sensor for detecting FA

[0125] Figure 16 These are spectra of a fiber optic sensor in formaldehyde solutions of different concentrations at room temperature. With the addition of formaldehyde solution, the intensity of the interference peak changes significantly. The light intensity and formaldehyde concentration show a good linear relationship, with a fitting coefficient of 0.9801. Considering the spectrometer resolution of 0.02 nm, the calculated detection limit for formaldehyde is 6.9 × 10⁻⁶. -8 Compared to direct probe detection of formaldehyde solution, using a fiber optic sensor to measure the formaldehyde detection limit can reduce it by several orders of magnitude. Compared to other similar works (Table 3), this invention has significant advantages in formaldehyde detection. This fiber optic formaldehyde sensor has the advantages of good selectivity, ease of operation, and a low detection limit, enabling the detection of ultra-trace levels of formaldehyde.

[0126] This invention designed and synthesized a decaborane derivative, M1, determined its molecular structure, and characterized its fluorescence properties. The M1 molecule exhibits a significant fluorescence response to formaldehyde, thus it can be used for formaldehyde detection. Results show that the detection limit of the M1 probe for formaldehyde in solution is 4.18 × 10⁻⁶. -6 Based on this, an optical fiber sensor based on the M1 / PMMA sensing film was constructed, which can reduce the detection limit of formaldehyde to 6.9 × 10⁻⁶. -8 Compared to similar formaldehyde probes previously reported, the M1 probe exhibits a significant advantage in detection limit. The M1 probe was used for formaldehyde detection in actual samples with satisfactory results. The fiber optic formaldehyde sensor designed in this invention possesses advantages such as high sensitivity, low detection limit, and good selectivity. This invention opens up a new avenue for formaldehyde detection.

[0127] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde, characterized in that, This includes broadband light sources, fiber optic sensors, and spectrometers; The broadband light source is used to generate incident light, and the spectrometer is used to collect and process optical signals. The fiber optic sensor includes three single-mode optical fibers and two coreless optical fibers, which are connected sequentially in the order of first single-mode optical fiber, second coreless optical fiber, third single-mode optical fiber, fourth coreless optical fiber, and fifth single-mode optical fiber. The surface of the third single-mode optical fiber used for sensing is coated with a sensing film and serves as the sensing fiber. The film-forming solution of the sensing film contains a decaborylformaldehyde fluorescent probe solution. The incident light emitted by the broadband light source passes through the sensing fiber coated with a sensing film, and the output light is collected by the spectrometer. The second coreless fiber acts as a beam splitter to disperse the incident light emitted by the broadband light source. When the incident light passes through the sensing fiber, more than half of the light still propagates in the core of the sensing fiber, while the other part of the light propagates in the cladding of the sensing fiber. The light propagating in the cladding is controlled by the sensing film. When the two beams reach the fourth coreless fiber, they interfere with each other. Finally, the interfering light is collected by the spectrometer and the interference spectrum is output. The decaborylformaldehyde fluorescent probe was synthesized through the following steps: Decaborane was dissolved in dry benzene and stirred at room temperature until completely dissolved. Diethyl sulfide was then added to obtain a pale yellow-green solution. The mixture was heated under nitrogen protection and maintained for a certain time to allow the reaction to complete. After the reaction, the solution turned yellow. After cooling to room temperature, diethyl ether and pentane were added, followed by cooling with ice. A large amount of white crystals precipitated. After vacuum filtration, [(C₂H₅)₂S]₂B was obtained. 10 H 12 ; Weigh out [(C2H5)2S]2B respectively 10 H 12 5-NH2C9H6N is dissolved in dry benzene, and after both are completely dissolved, [(C2H5)2S]2B is added. 10 H 12 The mixture was added to a 5-NH2C9H6N solution and reacted at room temperature for a certain time under nitrogen protection. After the reaction was completed, the solvent was obtained by filtration and the solvent was evaporated to obtain the crude product. The crude product was passed through a column a certain number of times to obtain the final product, the decaborylformaldehyde fluorescent probe. The reaction formula is as follows: B 10 H 14 +(C2H5)2S→[(C2H5)2S]2B 10 H 12 [(C2H5)2S]2B 10 H 12 +5-NH2C9H6N→(5-NH2C9H6N)2B 10 H 12 +(C2H5)2S The fabrication of the sensing film of the fiber optic sensor includes: Preparation of film-forming solution: PMMA was dissolved in dichloromethane solution, decaborylformaldehyde fluorescent probe solution was added, and the solution was ultrasonically treated to obtain a homogeneous solution; Fabrication of the sensing film: First, a groove capable of accommodating the sensing optical fiber is constructed on a polytetrafluoroethylene (PTFE) plate using hot melt adhesive; the clean optical fiber is fixed on the PTFE plate, and the cladding of the sensing optical fiber in the middle is etched with HF for a certain period of time, followed by rinsing with ultrapure water a certain number of times; the film-forming solution is dropped into the groove, and the optical fiber is slowly and uniformly rotated at a constant speed for a certain period of time; finally, the obtained sensing optical fiber is placed in the dark for a period of time.

2. The decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde according to claim 1, characterized in that, The decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde also includes a programmable temperature controller for temperature control. In use, the fiber optic sensor is placed inside the programmable temperature controller.

3. The decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde according to claim 1, characterized in that, The decaborylene fiber optic fluorescence sensor uses fluorescence titration to determine the detection limit of formaldehyde: multiple sets of decaborylene formaldehyde fluorescent probe solutions are prepared and their fluorescence intensity at 549 nm is measured, and the standard deviation of the blank sample is calculated; the fluorescence intensity at 549 nm of multiple decaborylene formaldehyde fluorescent probe solutions after reacting with formaldehyde is measured, and the detection limit of formaldehyde can be calculated using the following formula: Where σ is the standard deviation of the blank sample, and κ is the slope of the curve of fluorescence intensity at 549 nm versus formaldehyde FA concentration. The detection limit of the decaborylene fiber optic fluorescence sensor for detecting low concentrations of formaldehyde is calculated using the following formula: Where λ is the wavelength, C is the formaldehyde concentration, and S... C denoted as the sensitivity of the fiber optic fluorescence sensor, and ∈ represents the resolution of the spectrometer.

4. The decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde according to claim 1, characterized in that, The third segment of single-mode fiber used for sensing in the fiber optic sensor is 25mm long, and the coreless fiber is 10mm long.

5. The decaborylene fiber optic fluorescent sensor for detecting low concentrations of formaldehyde according to claim 1, characterized in that, The optimal pH value for the decaborylformaldehyde fluorescent probe to detect formaldehyde is 7.4.

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